Fluid metering system



Jan. 27, 1959 H. GOLD ETAL FLUID METERING SYSTEM 3 Sheets-Sheet 1 Original Filed March 14, 1947 A 2 0 wvm HWMMJ 4 3 FIG. 3'

HAROLD GOLD DAV/D M.' STRAIGHT @M MPJW Jan. 27, 1959 H. GOLD ET AL 2,870,777

FLUID METERING SYSTEM Original F..led March 14, 1947 5 Sheets-Sheet 2 HARO/.0 60.1.0 DAV/o M. snm/@Hr Jan. 27, 1959 H. GOLD ETAL 2,870,777

' FLUID METERING SYSTEM Original Filed March 14, 1947 3 Sheets-Sheet 3 DAV/D M. STRAIGHT 'M /MJW www nited States FLUID METERING SYSTEM Harold Gold, Shaker Heights, and David M. Straight, North Olmsted, Ohio The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the pay ment of any royalties thereon or therefor. e

This application is a division of our copending application Serial No. 734,840, filed March 14, 1947, now Patent 2,809,653, dated October l5, 1957.

This invention deals generally with the metering of fluids to or from a plurality of flow passages.

Specifically, the invention relates to devices for uniformly proportioning flow of fluid such as liquid fuel from a common source to a plurality of outlets, or from a plurality of sources to a common outlet, irrespective of differences in discharge pressures of the outlets or sources, or variations in fluid flow rates.

The invention will hereinafter be specifically described as embodied in devicesffor controlling fuel distribution in gas turbine engines, or for regulating flow from a plurality of fuel tanks so that all of the tanks empty `at the same rate. However, it should be understood that the invention is not limited to the illustrated uses or ernbodiments, being generally applicable for the automatic control of fluid flow.

In gas turbine engines, fuel is pumped from a source into a manifold from which it flows to various atomizing nozzles to be discharged into a combustion chamber. The flow rate from the manifold to each nozzle is controlled by the nozzle, but the requirements for a wellatomized discharge renders very difiicult'the matching of the nozzles for equal flow distribution. Further, the malfunctioning of one of the nozzles will greatly dis turb the flow rates to the remaining nozzles. A device to automatically control the rate of flow of fuel in each branch conduit from the manifold to the separate nozzles in such a maner that fuel flow is rendered independent of discharge nozzle variations is highly desirable. The present invention provides such a device which operates by automatically controlling the static pressure drop across matched metering orifices located in each branch conduit.

In the feeding of fuel from a plurality of tanks in an aircraft to the aircraft engine, it is highly desirable that each of the tanks empty at the same rate so that load conditions in the airplane will be balanced. The control devices of the present invention also function to so balancev the flow rate from a plurality of tanks that the tanks will empty at the same rate.

An object of the invention is to provide a device which I Will control the distribution of fuel to any number of discharge nozzles in a gas turbine engine or the like.

Another object of the invention is to provide a device which will maintain predetermined perfect distribution of fuel from a single source to a plurality of nozzles irrespective of uneven discharge nozzle pressure and variations in fuel flow rates.

Another object of the invention is to divide a supply of fluid into a plurality of parts maintained in constant relationship by flowing each divided fluid stream through a separate orifice and automatically throttling the streams tnt in accordance with variations in pressure drops across the orifices.

A still further object of the invention is to provide a method of dividing a supply of fluid into a plurality of equal or predetermined proportioned parts by flowing the fluid along a plurality of separate paths and through a .separate orice in each path having a predetermined reintake manifold arrangement for a plurality of discharge nozzles in a gas turbine engine with a separate orificed flow path between each nozzle andthe source of supply, and with a diaphragm-controlled metering valve actuated by departure from equality ofthe pressure drops across any of the orifices to nullify said departure and main- `tain constant flow rates in all of said paths irrespective of nozzle discharge pressures and malfunctioning of the nozzles.

A still further object of the invention is to provide a pilot regulator for a fluid distribution system wherein fixed orifices in series in a flow path of the device determine the pressure on an actuator for throttle valves controlling flow in other paths of the device and thereby maintain constant flow rates in said paths irrespective of variations in pressures of said fluid fed to the orifices.

Another and important object of this invention is to maintain a predetermined distribution relationship of volumetric flow rates in separate conduits throughout a wide range of flow conditions.

Anotherimportant specific object of the invention is to maintain a constant flow relationship in a plurality of branch con-duits throughout a wide range of flow rates so that fuel nozzles in a gas turbine engine will discharge identical amounts of fuel throughout a wide range of fuel flow.

Other and further objects of this invention will be apparent from the following detailed descriptions ofthe annexed sheets of drawings which diagrammatically illustrate various embodiments of the invention as examples of devices within the scope of the invention.

On the drawings:

Figure l is a diagrammatic elevational View with parts in Vertical cross section illustrating one system according to this invention for uniformly distributing fuel to a plurality of fixed orificevjets for a gas turbine engine.

Figure 2 is a diagrammatic view similar to Figure 1 but illustrating distribution of fuel to a plurality of springloaded diaphragm nozzles or jets for a gas turbine engine.

Figure 3 is a diagram-matic elevational View, with parts in vertical cross section, illustrating a distribution system according to this invention for uniformly emptying a plurality of fuel tanks to supply fuel to the carburetor of an aircraft engine so that equal balancing of the fuel load in the airplane will be maintained.

Figure 4 is a diagrammatic elevational View, with parts in vertical cross section, illustrating still another system for equally distributing fuel to a plurality of fixed orifice jets or nozzles which system has an increased operating range.

Figure 5 is a view of the system of Figure 4 arranged for equally emptying a plurality of tanks to maintain balanced fuel load distribution in an airplane or the like.

As shown on the drawings;

In Figure l, the reference numeral 10 designates genorally control, apparatusV fon enuallyv distributing. liquid fuel F from a supply tank lll to a plurality of fixed orifice jets or nozzles l2, l2. These nozzles supply the fuel to the combustion chamberI ofA a; gas turbine engin-ez` (not shown) and it is important that the combustion chamber receivesI identical amounts,y of fuel from each nozzle throughout. a wide range of fuelflow.

A pump lf3-pressures fuel fro-rn the. tank 11. into: a manifold` passage "d ofk the apparatusltb'tront which the fluid flows through aplurality. or" distributing-passages 2.5 l

(one for each nozzle) andthence'through s. meten' lr6. in eachI passage l' toa chamber 7 boundedon one side,v by a lrnp.- diaphragm t8. carryingy a valve. plug i9 which, controlsvv flowA tnrough. an orice 2Q. tor af passage 21 extending-to thenozzle E2. The, vavc'pl aslotted or grooyed cylindrical end: Z191 snug J sli in; the orifice Ztl and connected through a` rod portion lvlzzwith-` a second cylindrical portionlc snuglyA slidable in a seat 22. A passageway Z3 connects thechambenf? with the` bottom tacez of the` cylindrical. portion we whereby the static fuelpressure'in chamber t7 isr cause to action-the entire area of thediaphragm i8: The areas of the cylindrical portions 19a and'19c, exposed` tothe passageway 2l, are equal' so that the forcesY resulting from static fuel pressure inthe passageway 2larebalanced. The cylindricaljportion dahas groovesorslots 24 extending 'iongitudinally thereot` at spaced, intervals around itsperiphery, andthese grooves areiclosed. attheir upper ends by a head 19d on the top of the cylindrical portion.- The lower ends of the grooves communicate n through the bottom of the cylindrical portionzto discharge into the-passageway 2l. The grooves 24 provide metering passages through the orice 2@ and the tlow rate through the orifice is determined by the proportion. of the upper ends of the grooves that is exposed to the chamber 17. A washer 25 is bottomed on the head 19d of thefplugand underlies the central portion of the diaphragm 13; A second washer 26 overlies the diaphragm Sfand a nut 27 threaded on the threaded upper end we of the plug clamps the washers 25 and 26 on the diaphragm and anchors the plug valve to the diaphragm,

A- chamber Z9 is pro-vided above each diaphragm tti and is separated from the chamber i7 by the diaphragm.

A pilot branch passage also extends from. the. manitold passage M and contains a pilot orilice 3l whi-:hdischarges into a chamber 32. The chamber 32,. in turn, discharges through a jet oriicea into a passagers/ay 35.# communicating with the fuel tank l1.`

The chamber-?; is connected through a passage 35 with'each chamber 29. Thus the static fuelpressures in each chamber 29are at all times equal to the static fuel pressure in chamber 32. The diaphragms l acted on by the-fuelfpres-sure'in chambers 29 position the valve plugs lfuntilthe staticpressure in each chamber 17 is equal to the staticpressure in chamber 32, Any change in resistance to fluid tlow in any of the'discharge passages Zlwll be transmitted back as a change in pressure in the; cl'iamber i7. which feeds the particularV passage 2l. This change in pressure causes the diaphragm l2 to alter the.l position of the plug valve 19 varying the free area through the slots 24 thereof until the pressure balance between the chamber i7 and the chambcr'zZ is restored. The static pressures on the downstreaml side of each metering jet .te are therefore maintainedecual. Since the manifold passage dis relatively large,y the eectoit duidfriction is negligible and all of the branch metering j etsAv le. receivcthe fuel at the same static pressure'.l The static pressure. drops across each metering jet 16 are therefore maintained-equal, independently of diterences in resistance to fluid ow of any of the passages 21 or jetnozzlesl l2.

Whenrit is desired to maintain equal ratesof owin. each passage 2.1, as in the applicationof 'this system to a multi-jet gas-turbine engine; the,branch-;metering.jets 161l are provided Withequal orifices; ln otherfapplicationswhereitmay hedesiredto maintainadenite ratio, other than unity, between the rates of ilow in each passage 21, it is only necessary-'to use branch metering jets 16 which have orifices sized for giving the desired flow ratio.

The ratio of rate of ow through the passage 34 back to the tank 11 to the rate.of.ow in any of the passages 2l to the nozzle. l2 is maintained ata. constant ratio which is determinedby the ratioV of the orice areas of the pilot-'metering jet 31 to the branch metering jets 16. The passage 34 therefore could, if desired, be used to ly another jet nozzle 12... In the application of this system to the gas turbine engine', it is preferable; however,

to return the flow from passage 34-to the.` fuel tank 11.

The pressure in pilot regulator chamber 32 must be maintained higher than thek pressure in any ofthe'passages 2l and therefore the range of operation of the systern of Figure 1 is limited by the ability of the p ilot regulator jet 33 to maintain this higherpressure inthe chamber 32.

Since the nozzles 12 in theV systemfof'v Figure l have lixed orifices, a fixed pilot regulator jet" 33 will be endicient to maintain a pressure in they chamber 32 greater than the pressures in the passages 2li. However, it-xed jet nozzles are replaced with spring-loaded diaphragmoperated nozzles which do-not discharge until a predetermined pressure is built up against their diaphragms and whichtlren discharge at a constantly increasing ilow rate as pressure increases, it isnecessary to supplement the .pilot regulating jet 33 with a spring-loaded diaphragmoperated device similar to the nozzle.

A systemaccording to this invention for use with springloaded diaphragm-operated'nozzlesv4u1is shown in Figure 2, whereirrpartsy identical with parts described in'igure l have. been marked with the same lreference numerals;

In. the system of Figure 2; the conduits deining; the passages 2 receivenozzle housings 4lon their outer ends. Thesehousings-are centrally apertured and have annular chambers 4Z communicating with the passages 21x'. A tubular body 43 projectsthrough each housir'igy et and has ports 44 in its side wall communicating with` the annular passage. 42. The bottom end or`r the tubular member lrtflfhas a valve sent-5 thereon, whit/:thc upper end of themember'is closed by a'diaphragm de; Al cap 47 clamps the diaphragm on the member 43. The-cap is vented to the atmosphere as-at 4S and bottoms-'a coil spring 49 which acts on an adjustable nut Sti on-a stem 5ta of a valve member 5l. The stern 5in projects through the central portiony of the diaphragm 46. The vals/einem ber Si slides in the body "rtan'd'hasV @needle-like bottom end Sib coacting with the= seat @5f to close thelnozzl'e.V The. main body of the'valvehas grooves die' along-the length thereof for feedingv fuelfrom-the ports 4tft-tothe valve seat 'afas well asto achamberf 52" closed bythe diaphragm 4%. The spring-t9 loads-tbe valve-memberl so that it will remain on its seat45until a predetermined pressure has been-built up in the diaphragm chamber, whereupony the diaphragm will be forcedupwardlyto lift the valve ottits seat dandlopen'themetering passages c for discharge.

Since the nozzle 40 will notf open until apredetermined-pressure has been built upf-inA the passages 2l, and sincethe flow rate ofdischarge throughv the nozzlewill then increase in direct proportion to the increase in pressures in the .passages'ZItg the pilot' regulator jet 35 alone may not be suliicient to'maintain a pressure inchamber 32 which is-higher than pressures in the passages 21; and therefore a spring-loaded diaphragm-operated metering valve 55 is-provided in-the discharge passage 34-between the pilot regulator jet and the tank 1L This valve V55 can be. identical'with the nozzles 40 and is so shown. The Valve 5S will 'coact with the pilot regulator jet33 to hold ya .sufficient back pressure in the chamber'325that1islalways greaterthanthe pressures in the passages 21; Therefore; evenv at'lowfowrates; the pressure in chamber 32 will behigherfthan pressures in the passag'esZl.

The system of Figure 2 operates in the same manner as that described above in connection with Figure 1, and the pump 13 can be run at variable speeds throughout a relatively wide range for varying ow rates and the jets and throttle valves 19 will equally distribute the uid to all of the passages 21 irrespective of the changes in flow rates as determined by the pump 13.

In the embodiment shown in Figure 3 the apparatus 19a is arranged to control the ow from a plurality of sources to a single outlet so that tanks or the like will be emptied at the same rate to maintain balanced load conditions on an airplane or the like.

In Figure 3 a plurality of fuel tanks 60 are each equipped with a centrifugal-type booster pump 61 discharging into passages 62. Another tank 63 has a separate booster pump 64 discharging into a passage 65. The tank 63 may be considered the pilot tank, and the other tanks 60"are caused to discharge at the same rate as this pilot tank.

The passage 65 ha`s a iixed metering jet 66 therein discharging into a chamber 67 of the apparatus 10a, and this chamber 67 discharges through a pilot-regulating jet 68 into a branch passage 69 which, in turn, empties into a manifold passage 79.

The passages 62 each discharge through a throttle valve 71 into a passage 72 communicating with a chamber 73 which chamber, in turn, discharges through a fixed metering jet 74 and branch passageway '75 into a manifold passage 70. The chamber 73 is bounded on one side by a limp diaphragm 76 which, as explained hereinabove, is connected to the throttle valve 71 by washers and the like. The throttle valve 71 has cylindrical portions 71a and 71b respectively slidably seated in an orifice 77 and a passage 78. The cylindrical portion 71a has Slots 79 metering flow from the passage 62'to the passage 72 in amounts determined by the extent of exposure of the ends of the slots to the passage 72. The valves 71 are balanced in the same manner as the valves 19 described in the other embodiments of the invention.

A chamber 89 is provided above each diaphragm 76 and each chamber 80 is connected by a conduit passage 81 with the chamber 67.

The pump 64 pressures fuel through the jet 66 into the chamber 67 and \the regulator jet 63 maintains the fuel under pressure Lin this chamber 67. The pressure of chamber 67 is transmitted through the passage 31 to each of the chambers 80. The pressure in the chambers 89 acts on the diaphragms 76 to open the throttle valves 71 but this action is resisted by the pressure in the chambers 73 on the other sides of the diaphragms. The pressure in each chamber 73 will change whenever the pressure drop across the branch metering jet 74 changes. Since each branch metering jet discharges into the same manifold passage 70 as the pilot regulating jet 68, which maintains pressure in the chamber 67, it is evident that any variation in the pressure drop across the pilot metering jet 66 will immediately be reflected yin a pressure change in the chambers 0 thereby changing the setting of the throttle valve and maintaining a constant ow ratio in the passages 62 and 65. If the sizes of the metering orifices are equal, the ow rate in each passage will be identical as determined by the pump 64 and by a positive displacement fuel pump S2 receiving fuel `from the manifoldV 7i) and discharging into the carburetor S3 of an aircraft engine 84 for admix'ture with air from the air scoop 85 to form the fuel charge for the engine.

The system of Figure 3, therefore, operates in reverse relation relative to the systems of Figures 1 and 2.

In the embodiment of Figure 4, the apparatus 111e distributes fuel F from the tank 11 to a plurality of xed orifice nozzles 12 Without circulating the fuel back to the tank, as in the embodiment of Figure l. The manifold passage 14 of the apparatus 19C has the same branch passages 15, jets 16, chambers 17, limp diaphragms 13, throttle valves 19, orifices 29, passages 21, seats 22, and

passages 23 as the apparatus 10 of Figure 1, together with chambers 29 above the diaphragms 1S. The pilot branch passage 30 also extends from the manifold 14 and discharges through the pilot orifice 31 in the same manner as described in Figure 1, but a chamber 99 receives the fuel from the jet 31 and discharges through a jet 91 into a chamber 92 communicating through a passage 93 with one of the nozzles 12 and containing a limp diaphragm 94 carrying a shutoi valve 95 adapted to coact with 'a seat 96 in the entrance mouth to the passage 93. A chamber 97 is provided above the diaphragm 94.

The chamber between the jets 31 and 91 is connected through a passaged conduit 98 with each of the chambers 29.

The chamber 97 is connected through a passaged conduit 99 With check valves 106 interposed between the passages 21 and the conduit 99. Each check valve 100 includes' a limp diaphragm 101, which may be a part of the diaphragm 18, coactng with a seat 1112 controlling flow through a passage 103 to the passage 21. The diaphragm 101 is exposed on one face to a chamber 164 and on the other face to a chamber 195, both of which are connected to the conduit 99.` When pressure in the conduit 99 is greater than pressure in the passageway 21, the diaphragm will be forced downwardly against the seat 192 to close the passage 103 as shown in the lower valve 160 of Figure 4. When pressure in the passage 21 is greater than pressure in the conduit 99, thediaphragm 101 will be raised oft' of its seat 102 to the open position shown at the top of Figure 4. When the pressure in any of the passages 21 is greater than prevails at any given time in the conduit 99, the check valve 100 asso- -ciated with such passage 21 will open and thereby effect communication with, and equalization of the pressure in, the conduit 99. At the same time the remaining check valves 11D9, associated with the passages 21 that are at a lower pressure are closed. By this arrangement, therefore, the pressure in the conduit 99 and therethrough in the pilot chamber 97 is at all times equal to the highest pressure in any passage 21. The diaphragm-operated shut-olf valve will be positioned by the diaphragm 94 to balance the pressure in chamber 92 with the pressure in chamber 97 and conduit 99. Any pressure acljustment thus effected will bereflected in the pilot chamber 90 and thence through the conduit 98 in the diaphragm balancing chamber 29 to effect corresponding adjustment of the respective throttle valve 19. Thereby the pressure drop across any throttle valve 19 will always be equal to or. greater than the pressure drop across jet 91 so that the throttle valve 19 will not have to have an area greater than that of the jet 91.

The conduit 99 also communicates with another check valve 196 which is so arranged as to permit flow from the conduit 99 into the chamber 90 but to prevent flow from this chamber 9i@ into the conduit 99.' Thus the check valve 166 has a diaphragm 107 coacting with a seat 108 on the discharge mouth of the conduit 99 and connected with a passage 169 communicating with the chamber 99 and conduit 93 to relieve the pressure in conduit 99 when the apparatus is not operating.

During operation of the apparatus 16C, the pressure in chamber 90 is normally higher than the pressure in the conduit 99 and the check valve 106 remains closed. lf the pressure in passage 93 should be higher than that in any passage 21, the'diaphragm-operated valve 95 will move to a wide open position. This valve 95 should preferably be arranged so that it offers very little restriction to ow when Wide open thereby keeping the pressure drop across the distribution control toa minimum. If the pressure in the passage 93 drops materially, the diaphragm valve 95 will move to a closed position in ac- -cordance with the pressure in the chamber 97.

The device 10c yof Figure 4 therefore functions like the device 19 ot Figure 1 to divide the flow from the mani fo'ld L4 into a. plurality of' separate paths discharging through fixed orifices and'iiowingto the discharge nozzles under' the control' of diaphrag'mla'ctuated throttle valves which are automatically adjusted Whenever the pressure dropsacross the orifices vary relative to each other. The throttling4 valves are under control of -a pressure maintained between two fixed orifices by fuel flowing through still another branch passage t another nozzle. Flow to this other' nozzle is under control of a diaphragmoperated valve which is automatically positioned to maintain pressure in the feed chamber to this nozzle equal to the pressure ofthe highest pressured nozzle passage. rIhe arrangement of Figure 4 increases the' operating range for the pump 13 since the pilot system can maintain the pressures in the chamber 9G' above the pressures in the chamber 29, being augmented by the discharge pressures in the passages 2i..

In the embodiment' illustrated in Figure 5, parts identical with parts described in connection with Figure 3 have been marked with the same reference numerals. In Figure 5 the tanks 6i) are emptied by the pumps 6i through' the passages 62, discharging through the throttle valves 71 and orifices 74'into the manifold ti'undercontrol of the flow rate through the pilotorifices 66 `and 68 which maintain pressure in the pilotchamber 67 above the pressures in the diaphragm chambers 80. The pump 64 from the tank 63 flows fuel through' the. passage 65 and throttle valve 116 controlled by a diaphragm illbetween a chamber 112 exposed to the discharge from the throttle valve and a chamber 113. The chamber 113 is connected by conduit H4 to check valves H5 exposed to' pressure in the passages 62 and operating so that the conduit 114 will always be subjected to the lowest pressure in any passage 62'. Conduit H4 also communicates with a second' check'valve lil exposed. to pressure inthe pilot chamber 6'/ and operating so that the conduit Ile will `always at least be under the pressure of the chamber 67. This chamber 67 is also -connected by a conduit IIT with each' of the diaphragm chambers 80. The device 10d of Figure 5 operates in the same'manner as the device 19a of Figure 2 with the added feature of being accurate under higher pressure conditions and therefore operative over a larger range since the pressure in the pilot chamber 67 is always augmented by the discharge pressures in the passages 62and is under control of the diaphragm'valve 1li).

From the above descriptions it should be understood that theA invention provides various forms of apparatus forautomatically metering flow of uid in separate paths to maintain a constant relationship in the volumetric flow along said paths throughout a wide range of flow rates. The invention includes methods of regulating flowing streams of fluid relative to each other whenever variations in pressure drops of the streams as they flow through separate orifices is encountered. The pilot control for the system and method preferably includes a series of orifices establishing 'therebetween a control pressure forthrottling means' in other streams; In some forms, the pilot control includes a closed circulation of fiuid, in'other forms the pilot tiuid is not recirculated, and in still other forms the pressure built yup between the series of orifices is augmented by incorporation of an added flow regulator in the fluid circuit.

It will, of course, be understood that various details of construction may be varied through a' wide' range Without departing from the principles of vthis invention and it is, therefore', not the purpose to limit the patent granted hereon otherwise' than necessitated by tliesc'op'e of the' appended' claims. v

We claim as our invention:

1. Apparatus for fiowing liquid in predetermined w ratio from a plurality of sources which comprises means defining a flow path' for liquid from one source, said iiow path having a series of lorifices arranged to'develop a pressure head therebetween, means providing separate iiow paths for the liquid from all of the other of said plurality of sources, each of said other source flow paths having separate throttle valves and downstream therefrom separateorifices, means referencing said pressure head to said throttle valves to decrease the throttling effect upon an increase in said pressure head, and means effecting reference to the pressure of the liquid upstream from th'e orifices in said other paths and operative to resist the decrease in th'rottling effect of said throttle valves. i

2. In apparatus for' controlling the discharge rateof flowingliquid from each of a plurality of sources toa common receiver for the liquid, means defining a plurality of separate ow paths for the liquid from the sources, including' a first path serving as a pilot, means variably throttling the liquid iiow in said pilot path,

means downstreamfrom the throttling means in said pilot path providing a series of fixed orifices, means providing other respective flow paths for liquid from the remaining sources, variable throttling means in said other source paths, fixed orifices in said other source paths,vmeans for combining the liquid from all of the paths, means referencing the pressure of the fiuid in said pilot path between said series of fixed orifices insaid other source paths, and means for referencing each of said other source flow paths to said throttle means in said pilot path.

3. In apparatus for controlling the discharge rate of flowing liquid from each of a plurality of sources to a common lreceiver for the liquid, means defininga plurality of separate flow paths for the liquid fromthe sources, including a first path serving as a pilot, means variably throttling the liquid flow in saidl pilot; path, means downstream from'theV throttling means. in.V said pilot path providing a series of xed orifices,means.pro viding other respective liow paths for liquid from` the remaining sources, variable throttling means in said other source paths, fixed orifices in said other source paths, means for combining the liquid from all of the paths, Vmeans referencing the pressure of the liuid in said pilot path between said series of fixed orifices in said other source paths, means for referencing each ofv said other source flow paths to said throttle means in said pilot path, and means for referencing the pressure head bctween said series of fixed orifices to the throttle means in said pilot-path whenever the pressures in said other source paths fall below said pressure head.

Germany July 27,- 19,29 Great Britain May 7,- 1946 

